Electric discharge device circuit



P. c. MICHEL 2,407,505

ELECTRIC DISCHARGE DEVICEQIRCUIT Filed April 4; 1942 2 Sheets-Sheet 1 Inventor: Philip C.Mich e\,

is Attorney.

QNRSBQ mun Sept. 10,1946;

R Nu m i i Sept. 10, 1946. P. mam-:1. 2,407,505 I ELECTRIC DISCHARGE DEVICE CIRCUIT Fileql April 4, 1942 2 Sheets-Sheet 2 l/V/T/A TING .I/GNAL b'O/SE TERM/M TIA/6 SIGNAL 14/0/85 H //2 rfi //l E L I M L4 AF- vInv erwcoqrw Philip C.Michel,

y His Attorney.

Patented Sept. 10, 1946 ELECTRIC DISCHARGE DEVICE" CIRCUIT Philip 0. Michel, Schenectady; N. Y., assignor: to General Electric Company, a corporation of New York Application April 4, 1942, Serial No. 437,627

Thefpresent application is a continuation-inpart of my copending' application, Serial No. 419,- 035, filed November'13, 1941, Patent No. 2,324,- 314', datedJuly 13; 1943, and assigned. to the same assignee as the present application;

My' present invention relates to circuits employing electric discharge devices or electric valves and concerns particularly arrangements for: use in impulse c'ounting'and interval timing;

It is an object of my'invention to provide improved: arrangements" for' transmitting impulse signals to impulse responsive devices withincreased precision withregard to'the instant of actuation of the impulse responsive device. and with high accuracy and' relia'bilitywith regard to the rejection of spurious signals:

Another object of my invention islto' provide impulse transmitting arrangements which may readilybe adjusted for various degrees of spurious signal rejection, and which are provided with arrangements for testing the impulse transmitting circuits together with the impulse responsive'devices, counterszonintervaltimers associated" therewith.

Other and furtherobjects and. advantages. will become apparent as. the following description proceeds,

The apparatus to which the present application relates may be used, and is particularlyuseful, in conjunction with on and oif. control impulse-producing devices-employed to measure time intervals. Relatively: short time intervals may be measured accuratelyby' counting the number of cycles of a. source of highconstant frequency impulses which are produced during the time interval betweentwo control impulses. A switching unit is.- interposed between the high frequency cyclegenerator and a" cycle counter and the switching unit is designed: to turn on and off in response to the twoxsucoessive controlimpulses. The apparatus t'o'which the presentapplication relatesis: particularly useful for increasing the accuracy with which control impulses are applied 'to' such a' switching unit.

However, my invention is not limited to this particular application nor to the particular apparatus shown and described:

The control impulses ordinarilytake the-.form of single cycles of voltage fluctuations such as might: be. produced by a magnet passing 3, ourrent-producing coil or a device making and reaking. aninductive circuit in proximity to such a coil. In order to produce high precision of operation of the switching: unit, it is desirable thatt'he switching unit be actuated-at the precise 9 Claims. (Cl. 250-27) instantithat control voltage-fluctuation impulses pass through zero'value or cross the zero line. It is also desirable to prevent the'switching unit from being actuated in response to spurious fluctuation which maybe produced by stray inductive'effects in conductors. carrying the genuine control'impulses. Such. spurious voltage fluctuationsare frequently referred to as noise.

In carryingout my invention in its preferred form I provide a pair of input terminals to which a pair of insulated. conductors may be connected or coupled. These: conductors. carry the control impulses from the source at which they are generated. Since itmay" be necessary that these conductors be of appreciable length; they have a tendency to pick up voltage. with respect to ground. For eliminating such line to' ground voltages or noises, I interposei a signal amplifier and line to ground attenuator between the input terminals and a second pair of terminals referred to as intermediate't'erminals. Between'these intermediate terminals and thefinal output terminals two different circuits are provided, one including a voltage diiferentiator and theother including a voltage integrator; The final output terminals here referredfto are connected. to the control terminals of the switchin unit. These two circuits actually terminate in the control electrodes of a current-controlling device having two' different control electrodes each of which must be maintained at a potential. exceeding a predetermined value in order'for the currentcontroll'ing deviceto pass current. The currentcontrollingdevice is'operatively interposed in the circuit to the .output'terminals.

The first circuit between the said intermediate terminals and the current-controlling device also includes a clipper for converting the single-cycle input impulses into a square topped wave in addition to the difierentiator which'is for converting the square topped wave into a single sharp peak that occurs precisely at'the instant'of zero cross-over of the original wave. This sharp peak undifferentiated wave occurs between a pair of differentiated. wave: terminals. which are connected to one. of 'ther electrodes'of the currentcontrollingi device.

The-second circuit between the'said intermediate terminals and the-current-controlling device includes anintegrator'which produces a voltage a continuously proportional to the instantaneous time integral of the negative loop of the input sharp peaks produced at the differentiated wave terminals and transmits an impulse of like sharpness to the control terminals of the switching unit. I 7

A better understanding of the invention will be afforded by the following detailed description considered in connection with the accompanying drawings, and those features of the invention which are believed to be novel and patentable will be pointed out inthe claims appended hereto.

General description In the drawings Fig. l is an electrical circuit diagram schematically representing one embodiment of my invention, and Fig. 2 is a set of graphs illustrating the principle of operation of the apparatus.

In the drawings I have shown an impulse transmitting circuit or system utilized in conjunction with a switching unit I l for controlling the application of high speed counting impulses from a cycle generator l2 to a cycle counter 53. The present application does not relate to the elements H, l2 and I3, and these are represented schematically by rectangles. The cycle generator l2 mayibe any source of impulses of adequate frequency and constancy. The cycle counter l3 may be any cycle counting apparatus adapted to the counting of impulses of the frequency produced by the cycle generator l2 and may take the form, forv example, of the devices disclosed in my copending applications, Serial No. 400,075, filed June 2'7, 1941, and Serial No. 388,820, filed April 11, 1941. The switching unit ll may be any device which may be actuated in response to con trol impulses so as to: be turned on and off, or become conducting and non-conducting ,in response to successive control impulses so as to pass counting impulses from the cycle generator II to the cycle counter l3 during the interval between two successive control impulses. The switching unit may take the form, for example, shown in my parent application, Serial No. 419,035, filed November 13, 1941. If the frequency of the cycle generator I2 is accurately known, the cycle counter l3 may be employed for measuring the time interval between two successive control impulses applied between the control terminals 14 and I 5 of the switching unit I i.

' 'The control impulse terminals I l and I5 are the final output terminals of the impulse transmitting arrangement described in the present application. For receiving control impulses from a source (not shown) a pair of insulated conductors I6 is provided which may be connected directly or coupled indirectly to a pair of input terminals ll and it. Preferably, for permitting adjustment of the minimum voltage of control impulses which are to be passed by the impulse transmitting circuit, an adjustable gain control [9, in tlieform of a potentiometer, is interposed between the input lines of conductors l6 and the 4 input terminals l1 and I8. The mid point 29 of the potentiometer resistance is grounded.

For amplifying the desired impulses or control signals appearing across the input terminals l1 5 and I8 and substantially eliminating line to ground noise, a special amplifying circuit 2! is provided. The amplifierll has output or load terminals 22 and (the latter being the common ground) which represent intermediate terminals of the impulse transmitting apparatus of the present application. Sets of terminals are shown in various parts of the apparatus for convenience in describing the operation and are referred to as intermediate terminals; but it will be understood that such terminals need not necessarily be brought out in the actual apparatus except for the purpose of checking the operation thereof by means of a suitable voltmeter, oscilloscope, or the like.

For converting the amplified input impulse at the terminals 22 and 20 into a sharp peak occurring precisely at the zero cross-over point of the input wave, a circuit is provided including a clipper 23 and a difierentiator 24. The clipper 23 is connected across the intermediate terminals 22 and 29, either directly or indirectly. In the arrangement shown an'amplifier 25 is interposed. The difierentiator 24 is interposed between the clipper 23 and a pair of terminals 26 and 21 referred to as difierentiated wave terminals, the terminal 21 being shown as grounded. Consequently, in the arrangement shown the terminal 21 is electrically connected to the grounded point 2c of the input potentiometer 19, which serves also as one of the output terminals of the amplifier 2!. Preferably an amplifier 28 is interposed between the clipper 23 and the differentiator 24 and an amplifier 29 is interposed also between the differentiator and the differentiated wave terminals 26 and 21.

An integrator 32) is interposed between the intermediate terminals 22 and 20 and a pair of integrated wave terminals 3! and 21, the latter being shown as grounded and therefore common to the second differentiated wave terminal. Pref- I erably the amplifier 25 is interposed between the integrator 30 and the terminals 22 and 20 and another amplifier 32 is interposed between the integrator 30 and the integrated wave terminals 3| and 21.

For controlling the application of an actuating voltage of the shape appearing between the differentiated wave terminals 26 and 21 to the final output terminals 14 and I5 serving as control terminals for the switching unit H, a current-controlling device 33, arranged as a noise reiector, is provided. v'Ihe current-controlling device 33 is so constructed that it passes the differentiated wave appearing between the terminals 26 and 2'! only when the voltage between the integrated wave terminals 3| and 21 exceeds a predetermined value. If desired, an amplifier 341K135 be inter posed between the current-controlling device 33 and the final output terminals 14 and I5.

Noise limiting amplifier 21 The amplifier 2| comprises two stages of pushpull connected electric-discharge. devices which may be of the three element vacuum tube or-triode type. The first stage comprises a pair of triodes 35 and 36 and the second stage comprises a pair of triodes 31 and 38. Each triode has an anode, a cathode and a control electrode, designated by the customary symbols. The cathodes of the triodes 35 and 36 are grounded through ended the resistor 48. Ifline to ground noises of all frequencies are to be attenuated, the oath ode impedance 39 may take the form of a resistor. For increasing the attenuation at higher frequencies the impedance 39- may be madeinductive, and for relatively increasingthe attenuation at lower frequencies the impedance 39 may be made capacitive'in character. The triodes 35 and 36 are energized from a terminal through a pair of anode resistors 44 and 4.5,

The triodes 3! and 38 are connected in a mannersomewhat similar to the triodes 35 and 36 having their control'electrodes coupled to the anodes of the triodes- 35 and 36- andbeing energized from the terminal 43 through a pair of anode resistors. One ofthe anodes, for example, the anode'of the triocle 31 is connected to the terminal 22 which serves as one of the intermediate terminals of the impulse transmitting apparatus. The stage 3T-38 of the amplifier 2| produces further signal amplification and lineto-ground noise attenuation.

In order to obtain faithful amplification of very weak signals applied to the terminals [1, [9, the terminal 43 is preferably connected to a suitable" source of closely voltage-regulated direct current consisting of a unidirectional current source 47, a ballast resistor 48-and a filter choke 49 connected in series to the terminal '43- and with a filter condenser 59 connected'between the terminal 43 and the ground terminal. For voltage regulation a pair of voltage regulator tubes such as neon tubes may be connected between the ground terminal and the common terminal 53 of the resistor 48 and the choke 49. A resistor 54' may be connected across one of the tubes, e. g., the tube 52, in order to insure that the other tube, viz: 5|, will break down first when voltage is first applied from the source 41. Consequently, the voltage of the source 4! need not exceed that sufficient to break down one of the tubes 5| and 52, which have a considerably lower operating voltage at which they hold the output voltage. It will be understood that the resistor 54 is not a voltage dividing potentiometer of negligible conductance but a current-carrying element which is capable of causing the tube 5| to break down.

The amplifier 25 The amplifier 25 may take the'form of a conventional electric discharge device, being shown 'asa tetrode screen-grid vacuum tube with a bias resistor 55 connected in its cathode lead and a by-pass condenser 56 connected across the resistor 55. The tetrode 25 has a control electrode 51 1 I preferably has afilter circuit 25' interposed be!- tween its anode resistor and the, positive terminal 3+ of. the source. 46.

Clipper 23 The clipper 23, as shown. takesthe form of a pair of rectifying elements-.68. .and El having anodes82 and 63, and cathodes; 64 and i3l5Zrespec tively.. Thev rectifying elements 5!! and may be vacuum tube diode rectifiers such as type 6H6, for example. The diodes have electrodes: of opposite polarity in effect connected together. That is, the anode 6:2 of one diode andthezcathode 65 of the other diode are connectedto an intermediate terminal 65 and the remaining two electrodes 63 and 64. are grounded or connected to another terminal through biases of opposite polarity. Use of an independent biassourcegives least erratic action. However, one of the existing. biases may be. employed. In the arrangement shown the bias voltage sourceconsists of a biasing cathode resistor 51 connected in the cathode lead of the amplifier 28. The resistor 81 has a terminal 68 at a datum potential representing the a-verage potential of the electrodes 63 and 8 of the clipper 23, has a terminal: 69 of higher potentialthan the terminal 68 anda second terminal 10 at a lower potential than the terminal 68. The diode cathode 64 is connected tothe terminal 59 and the diode anode 63- is connected to the terminal 19 which in the arrangement illustrated is at ground potentiaI; The by-pass condensers H and- !2 are connected to the resistor 61 as shown. I

The clipper 23- is coupled to the terminal 59 of the amplifier 25 through a resistance-capacity circuit including a condenser 13, a resistor 14 between one plate of'the condenser and the clipper terminal 66, and a resistor 15 connected between the condenser 13 and the clipper terminal 68, the second plate of the condenser 53 being connected to the terminal 59 of the amplifier 25. The potential differences betweenthe terminals 69 and 68 and between the terminals 68 and 18 are so chosen that the maximum voltages between the terminals 68 and 66 will be considerably less than the maximum deviations from the average voltage of the terminal 59, so that a square topped relatively steep-sided wave will be produced between the terminals 68 and 66, which has a narrow sloping portion in relation to the time period of the. wave. I

The amplifier 28 may bean amplifier of conventional type comprising anelectric-discharge tube represented as a screen grid vacuum tube or tetrode with a cathode 1'! connected to the bias resistor 61, a control electrode 18 connected to the clipper terminal 65, a screen grid 19 'connected to a point at a suitable potential ina-conventional manner and an anode connected in series, with an anode resistor B! to the positive terminal of a source of anode potential which may be the positive terminal B+- of a common source 46. The point 68in the cathode bias resistor 6'! serves as the point of datum potential for the clipper 23, and the amplifier control electrode I8.

Dijferentictor 24 The difi'erentiator 24 comprises a resistor 82 of relatively small resistance connected in series with a condenser 83 of relatively small capacity between a ground terminal 85v and the anode terminal 80 of the amplifier 28 serving as another pair of ,intermediate terminals of the impulsetransmitting circuit. If desired another relatively 7 low-resistance current limiting resistor 84 may be connected in series between the resistor 82 and the condenser 83 for Voltage division; Thecom mon point 85 of the resistors 82 and 84 together with the ground terminal 86 serves as another pair of intermediate terminals. They may be used as a pair of differentiated wave terminals but preferably the amplifier 29 is interposed between the terminal 85 and the differentiated wave terminal 2B.

- The amplifier .29 may be a conventional electric discharge tube such as a triode vacuum tube. Preferably it is designed and connected so as to be zero Ibiased and grid limited for cutting off negative peaks to avoid the necessity for accurately controlling the amplitude of the input signal and to permit sharpening the signal in successive vacuum tube stages by small-time-constant resistance-capacity couplings. A Class B tube such as one-half of a type 6N7 may be employed, e. g., which will stand having grid and cathode tied together through a resistor. The characteristics are such that the tube operates between cut-off and the efiective plate-current saturation that results from the rectifying effect of the grid which tends to limit its rise in potential. As shown it has a grounded cathode, and an anode connected in series with an anode re,- sistor 8'! to a positive current source terminal, whichmay be the terminal B+ of the common source 46. It has a control electrode or grid 33 connected to the terminal 85 of thedifferentiator 24. Myinvention is not limited to specific constants and relationships. However, when using a plate current source 46 of 300 volts, I have obtained satisfactory operation of the tube 29 by making the capacity of the condenser 83 one hundred zmicromicrofarads, and the resistances of the resistors 82 and 84, one hundred thousand and fiity'thousand ohms respectively, when the time duration of negative impulses applied to the difierentiator between its input terminals 80 and 86 is anything from about thirty microseconds to a few hundred microseconds or more.

The amplifier 29 is resistance capacity coupled to the difierentiated wave terminals 29 and-21 through a condenser 89 and a resistor 90 which have a sufficiently small time constant to preserve the steepness of the differentiated-wave appearing between the terminals 85 and86-across the differentiator resistor 82. g j

Integrator 30 r r The integrator 30 comprises iundamentallya resistance capacity circuit of relatively large time constant which in its simplest form might consist of a relatively large condenser and a relatively large resistor connected in series between the input terminals 59 and a ground terminal 9 I which comprise the load terminals of the amplifier 25; the output terminals 92 and 9| of the integrator being terminals of the condenser. However, in order to provide for adjustability of the minimum effective period of signals to which the signal transmitting circuit will respond, the condenser connected between the terminals 92 and 9| is made adjustable. It takes the form, for example, of a plurality of condensers 93 each having a different capacity, grounded on one side and connected on the other side to stationary contacts adapted to cooperate with a movable contact 94 connected to the integrator output terminal 92. Also, to facilitate providing adjustability in the responsiveness of the impulse transmitting c'ircuit, a. coupling condenser 95 is interposed in a series conection of a resistor 96 of relatively large resistancefconnected between the terminals 59 and'92.

The output terminals 92 and 9| of the integrator-30 serve as the input terminals of the amplifier 32, which'may be an electric discharge device of conventional type shown as a screen grid vacuum tube or tetrode with a control electrode connected to the output terminal 92 of the integrator 30 and with a cathode grounded in 'a conventional manner through aby-passed bias resistor.

The amplifier 32' has a load terminal 91 connected to its anode .which is resistance-capacity coupled to the integrated wave terminals 3| and 2'1, the latter being a grounded terminal;

Noise rei'ector 33 The current-controlling device 33 is shown as taking the form of a plural grid electric discharge device such'as a BL? pentagrid vacuum tube, for example, arranged as a mixer amplifier. The amplifier 33 has five grids customarily designated by the numbers 1 to 5 consecutively from a cathode 98 to an anode 99. The #5 grid isconnected to the cathode 98 to serve as a suppressor grid in the conventional manner and the #2 and #4 grids are connected to a point of suitable intermediate potential in a conventional manner to serve as a shield for the #3 grid. The #1 and #3 grids are utilized as independent control electrodes, the #1 grid being connected to the differentiated wave terminal 29 and the #3 grid being connected to the integrated wave terminal 3|. The cathode 98 is connected through a bias resistor I00 to the ground terminal 21. Suitable by-pass condensers are provided as shown. The anode 99 is connected in series with an anode resistor IOI to a positive terminal of a source of anode voltage which may be the positive terminal B+ of the common source. The constants of the circuit of the amplifier 33 are so chosen that it will conduct current and transmit an impulse through its load terminal I02 D connected to the anode 99 only when both the potential difference between the differentiated wave terminals 26 and 21 and the potential difierence between the integrated wave terminals 3| and 2! exceed predetermined values. These values are respectively avalue below that which the differentiated wave between the terminals 26 and 21 is expected to attain in response to a desired signal impulse, and a value less than the maximum amplitude of the integrated waveproduced between the terminals 3| and 21 by a signal impulse having the minimum efiective period for impulses which are to be transmitted through the apparatus In this manner the device 33 serves as a noise rejector. The device 33 may be regarded as a coupling device controlled by the integrated wave at the terminals 3| and 21 for selectively coupling the differentiated wave terminals 2'6 and 21 to the load terminals I02 and 21.

For zero and infinity end points of the range of minimum effective periods of input signals to be passed, the movable contact 94 may have mechanically connected thereto a second movable contact I03 cooperating with a plurality of stationary contacts all of which are grounded except the last, which is designated by the numeral Hi4 and is connected to the cathode 98 of the amplifier 33. The movable contact I03 is connected to the integrated wave terminal 3| in series with a resistor I05.

The movable contacts 94 and I03, together with the stationary contacts form, a selector switch P for adjusting the minimum effective period of signal impulses to be passed. For the end points infinity and zero respectively of the switch for testing or checking purposes, two additional grounded stationary contacts MBA and H163 are provided which cooperate with the movable contact 94. In the infinity position no signals are passed and in the zero position all signals are passed.

The amplifier 34 may also be an electric discharge device of conventional type, being shown as a triode vacuum tube with a grounded cathode and a control electrode, resistance-capacity coupled to the load terminal I02 of the amplifier 33. In order to preserve the sharp character of the impulse signal transmitted through the amplifier 33, this coupling circuit is designed with a relatively low time constant comprising a relatively small condenser I! and a relatively low-resistance resistor I08 in series, with an additional relatively small resistor I09 interposed in series, if desired, for dividing the potential applied to the control electrode of the amplifier 34. If desired the amplifiers 34 and 29 may form two parts of a double triode vacuum tube as shown; Preierablythe amplifier 34 also haszero grid bias, and the circuit constants are such that the input signal swings the grid or contro1, electrode well beyond cutoff to produce a sharp piflse of positive polarity and having an amplitude and width essentially independent of the slope of the original signal at zero crossover. The amplifier 34 has its anode connected in series with an anode resistor to apositive terminal from a source of anode potential in any conventional manner and the anode is connected to a load terminal III! which is resistance-capacity coupled in any conventional manner to the final output terminals I4 and I which serve as the control terminalss of the switching unit II.

Operation in general The purpose to be accomplished by the impulse transmitting arrangement shown in Fig. 1 and the principle of operation will be understood more readily from the graphs of functional wave forms shown in Fig. 2. Each of the graphs of Fig. 2 represents a voltage wave and the waves are designated by the symbols E to E19, inclusive, which symbols are also applied to the points in the diagram of Fig. 1 at which voltages of such wave form appear. The apparatus for producing the input signals which are intended for actuating the control terminals I4 and I5 of the switching unit I I is not a part of the present invention and, therefore, need not be described. It will be assumed that an input signal of the wave form shown in E10 is received through the conductors I6 and applied to the input terminals I1 and I8. The potentiometer I9 is set at a value for controllingthe minimum amplitude E of input control signals to which the apparatus is to be made responsive.

Referring to Fig. 2 it will be seen that the curve E10 includes a voltage fluctuation I I I comprising one cycle which serves as an initiating signal, and a second single-cycle voltage fluctuation II2 which serves as a terminating signal. These two signals are .for first turning the switching unit on and then turning it oh. If desired the switching unit II may be of the type described aforesaid Copending application Serial No. 419,035, filed November 13, 1941, which is prevented from responding to more than two signal cycles unless reset. Referring to curve E10 again, it will be observed that there may be some ragged voltage fluctuations I I3 which are irregular in wave form and occur before or after the initiating signal II I and which might cause false operation of the switching unit II if the switching unit II were permitted to respond to such spurious voltage fluctuations IIS. Owing to the fact that such spurious voltage fluctuations are usually of ragged character and would produce a disagreeable sound which if the signal output were converted into acoustic vibrations, they are frequently referred to as noise.

Signal sharpening The problem of making the switching unit II respond precisely at the instant when the initiating signals I II and I12 cross the horizontal axis or zero point will first be considered. In order to steepen the portion of the wave in the vicinity of the zero cross-over point, it may first be con-' siderably amplified as represented schematically by the curve E11. If desired the amplification maybe even greater thanthat shown by the scale of the curves since the peaks are to be eliminated. The function of the clipper 23 is illustrated by the curve E12. It will be apparent that a greatly magnified wave such as E11 although originally somewhat resembling a sinusoidal wave form will become a square topped wave with a very nearly'perpendicular cross-over portion II4 as shown in curve E12, if the amplitude is limited to a fixed value relatively small in comparison with the original peak amplitude. The transmission of such a wave through a low time constant circuit such as the d'ifierentiator 24 results in the production of steep voltage impulses atthe vertical portions of the curve E12 as shown in curve E31. After such a wave is transmitted through the amplifier 29 it is further amplified, the negative peaks are cut off, and onlythe amplified positive peak E14 remains. It will be understood that in resistance-capacity coupled vacuum tube circuits having anode resistors or impedances the wave is ordinarily inverted by U each stage, i. e. has the polarity reversed because anode voltage rises when grid or control electrode voltage falls, and vice versa. However, the connections and characteristics of the tube 29 are .such that positive voltages applied to the' control grid 88 have relatively little effect. Since the tube employed is of the type uninjured by positive grid voltages, thegrid may be connected to the cathode through a resistor to give a zero bias. The tube is in efiect saturated at zero grid potential because the grid rectifies the input signal without forcing the anode potential to change appreciably. The resistor 84 limits the grid current. Consequently, no appreciable change in anode-cathode discharge current is produced by the positive loops of the differentiated wave between the terminals 885. In this manner the negative loops in the output wave at the tube anode are out 01f. The negative loops of the differentiated wave between the terminals 85 and 85, however, drive the grid negative and the anode positive. The constants are so chosen that the grid 88 is driven well beyond cutofi so that the anode is driven sharply positive. The small timeconstant of the resistance capacity coupling circuit 88-90, further sharpens the wave and results in a sharp positive peak between the differentiated wave terminals 26 and 27, there be- 11 ing but a single peak owing to the action of the tube 29 in cutting off the negative peaks. It is therefore unnecessary to have suficient time constant in the coupling 89-90 to reproduce the wave without overshoot, which would be neces-.

sary if the two positive peaks (negative in the output) of the wave applied to the control grid 88 had been retained. Successive further sharpening of the wave in the stages 33 and 34 is thus possible by use of low-time constant coupling circuits. Comparing the peaks of curves E and E14 it will be observed that a very steep sharp peak of high amplitude and exceedingly short duration is produced at the instant that the signal III or II4 cross the zero point. Consequently, the instant of actuation of the switching unit II is precisely fixed. 4

Noise reyection It will be evident that the various amplifications involved in the operation of sharpening the initiating signal unit I I will also have the effect of amplifying the noise voltage fluctuations II3. Accordingly, in order to guard against spurious operation of the switching unit I I, means are provided for preventing the current-controlling device 33 from passing a signal in response to steep voltage fluctuations such as those shown at II3. For this purpose wave forms such as shown in curve E are derived from signals ,I II and H2 for energizing the control electrode or #3 grid of the amplifier 33 during a period within' which the sharp signal impulse of E14 is to act. The voltage of the curve E15 is the negative integral with respect to time of the voltage of the signals III-and H2; The first half of a loop of the curve E15 between the points H5 and H6 is the integral of the negative loop'I ll of the initiating signal III. Geometrically it represents the area of the loop I H. The instantaneous value of the vertical distance from the horizontal axis to a point on the curve E15 represents the time integral at that instant of the initiating signal III. The constants of the mixer or multi-grid current-controlling device 33 are so chosen that the mixer passes the sharp impulse E14 only when the time integral of the negative lobe of the input signal voltage approaches the value where E is the minimum amplitude of an input signal which is to be accepted by the circuit and P is the minimum effective time duration of an input signal which is to be accepted by the apparatus. The value of E may be adjusted by the potentiometer I9 and the value P may be adjusted by the condenser selector switch P.

Adjustability of the degree of acceptance of the circuit is desirable for the reason that the switching unit I I is intended to be used for response to control impulses under widely diiTerent conditions of operation. For example, when the switching unit is used under conditions when the initiating signal and the terminating signal will each be of short duration and one closely following the other, it is necessary to adjust the apparatus for acceptance of input signals of shorter time duration than when the initiating signal and the terminatingsignal are separated by long time intervals. In this manner the apparatus may be so adjusted as not to respond to any noise impulses occurring before or between the two successive loops of the curve E15. It will be understood that adjusting the selector switch P for acceptance of 12 impulses of shorter time durationhas. the effect of decreasing the width, measuredin the horizon tal direction, of the lobe of the curve E15, so that.

the desired sharp impulse of curve E14 maybe passed; but any noise fluctuations shortlybefore or after the desired impulse will have no. effect.

It will be seen accordingly that after the volt. age of the wave form shown in curve E14 has been transmitted through the current-controlling device 33, it will take the waveform shown...in curve E16 from which the noise fluctuations have been eliminated. Owing to the difiiculty of accurately portraying the minute deviations in noise voltage to the scale used in Fig. 1, noattempt has been made to show the instant-to-instant variations accurately in the successive transformations of the curve I I3 in the graphs E-IB to EI5 and these curves "areto be considered merely as roughly indicative of the general na ture of the noise. It will be understood that the switching unit II is so designed that a sharp impulse I I I representing anv initiating signal raises a control potential therein and a sharp impulse Il2"representing the terminating signal lowers the control potential therein as represented by the curve E11. The counting impulses produced by the cycle generator I2 are represented schematically by the curve E13 (shown with less than usual frequency for clarity), and thecounter impulses transmitted by the switching unit I I from the generator I2 to the cycle counter I3 are represented by the curve E19. It will be observed that during the time interval between the peaks III and H2 the. counter impulses of the curve E19 are supplied to the cycle counter I3. An indication of the number of such cycles produced by the counter I3 serves therefore as an indication of the time interval between the initiating signal and the terminating signal.

Circuit testing For testing the noise pick-up of the line I6 and checking the operation of the apparatus the end points IIiIiA and IDBB oi the selector switch P may be used. When the contacts 94 and IOBA are together, the integratoroutput terminal 92 remains grounded, the integrated wave between theterminals 3i and 21 remains zero, and the tube 33 has its #3 grid permanently biased off so that no signals can pass. This. corresponds to infinite condenser capacity in the selector P or "acceptance only of signals having an infinite time dura-' tion. On the other hand, when the contacts 94 and IIZSB are together, and likewise the contacts I33 and IN, the .tube 32 remains biased off, but the potential of the#3 control electrode of the tube 33 is raised to cathode potential by connection thereto through the resistor I05, and any signal on the #1 grid is passed. This corresponds to acceptance of input signals of the zero minimum effective period. This. setting of the selector switch P may be used with a noise-free line to avoid change of setting for input signals of diiTerent minimum effective periods.

In order to test the accuracy of the impulse transmitting apparatus and also the elements i2, H and. I3, a test signal source may be provided. As illustrated in Fig. 1 I providea doublepole double-throw switch I I! with a pair of movable blades connected to the line I6 leading to the impulse transmission system input terminals I1 and I8. The switch I I! has a pair of stationary contacts H9 connected to conductors I20.such a telephone line, e. g., leading from a regular source of control impulses (not shown), ands.

173' second pair of stationary :contacts I2'I connected to a test signal source.

The test signal source comprises a pick-up coil I22 which is a current-conducting coil connected to the switch contacts I2I and which is mounted near the periphery of a rotatable disk I23, For producing a magnetic flux to react inductively on the pick-up coil I 22, a permanent magnet I24 is radially mounted at the edge of the disk I23. For driving the disk I23 at a uniform speed which may be held with great constancy, it is connected to a synchronous motor I energized .by an accurately constant frequency source of alternating current I26. For'checking the speedof the synchronous motor 125 a suitable device, such as a revolution counter and accurate clock, a tachometer or an accurate "frequency meter 121 is provided.

When it is desired to test the operation of the control counting apparatus the switch H1 is closed in a test signal position and the time interval between two successive transits of the magnet I24 past the pick-up coil I22 is determined by calculation from the speed of the synchronous motor I25 indicated by the frequency meter ,I2'I. Theproper functioning of the apparatus may be checked with the motor I25 running by connecting a cathode ray oscilloscope between ground and the various intermediate terminals in succession such as theterminals 22, 59, 66, 80, 85, 26, 92, 3I, and III for observing the wave forms.

Line noise attenuation The manner in which the amplifier '2I eliminates line to ground nois from the conductors I20 and II 6 will be understood from a consideration of the operation of the degenerative cathode resistors, such as the resistor 39 associated with the tubes and 36. A genuine input signal produces a potential difference between the conductors I6 and likewise between the control electrodes of the tubes 35 and 36. Accordingly the discharge current of one tube "is increased and that of the other 'tubeiis decreased and an amplifying effect takes .place in a conventional manner by reason of the fact that the increase in current in one anode resistor 44 and a decrease in the other resistor 45, or vice versa, produces a potential difference between the two anodes which is considerably greater than the difference between the two electrodes. Since one control electrode is raised in potential as much as the other is lowered and likewise the anode current of one tube is raised as much as that of the other is lowered, there is no change in the current flowing in the degenerative cathode resistor 39. Consequently, the amplifying ratio of the tubes is unchanged and the input signal is fully amplified. However, if line to ground noise were to be picked up by the conductors I20 or IIB, both control electrodes of the tubes 35 and 36 would be raised or lowered together and the current flowing in the degenerative cathode resistor 39 would be varied causing a variation in the cathode potential nearly equaling "the variation in control electrode voltage in each tube. Con sequently the residual grid-cathode voltage, greatly reduced, produces very little output or load voltage. In this manner, line to ground noise is attenuated, whereas the desired input signals appearing between the conductors l6 are amplified. This action is further enhanced by the second stage of tubes 31 and '38. The connections of the tubes 35 and 36, 31 and 38 also impulse transmitting .and cycle have the effect of balancing the signal :volta'ges applied to the conductors I6 in case they should be unsymmetrical with respect to ground. In this case the lack of symmetry causes :sufiicient variation in current flowingin the cathoderesistor 39 to balance the signal voltages with respect to the bias point-40' inthe control electrodes of the'tubes 35 and 35.

.I have herein shown and particularly described certain embodiments of .myinvention and "certain methods of operation embraceditherein for the purpose of explaining its practice :and showing its application, but it :will be obvious to those skilled in the art that many modifications and variations are possible and I aim therefore to cover all such modifications and variations :as fall within the scope of my invention which are defined in the appended claims What I claim as new and desire to secure Letters .Patent of the United States is:

.1. Apparatus .for producing a sharp'si'gnal impulse in response to a cycle of voltage fluctuation comprising a pair of input terminals adapted 'to have voltage fluctuations applied thereto, adevice connected to saidterminals for amplifying the voltage to steepen the portion'of the'volt'age cycle at the zero cross-over point, said device having two output connections, a pair of diode rectifiers connected in parallel with unlike electrodes together between the output connections o'f the amplifying device, and a pair of output terminals for the apparatus-one ofthe diodes being biased positively with .respect to :a datum potential, the other being biasednegatively withrei 'spect to a datum potential whereby "the voltage wave applied thereto is clippedat the positive and negative values corresponding to said lbiases'said diode rectifiers being coupled to said output terminals by a resistance capacity circuit .having'a relatively small product of resistance and capacity, said coupling circuit including a resistance connected between the output terminals and a condenser connected between one of the output terminals and one ofthe output connections of the amplifyingdevice, the second output terminal of the apparatus being connected 'to't'he second output connection of the amplifying'device.

2. Adiscriminator for preventing the response of an impulse responsive circuit to spurious volt-- age variations referred .to as noise, said apparatus comprising a pair of .input terminals to which a voltage is adapted'to be applied which is intended to fluctuate through one'cycle to represent each genuine input impulse, .a second pair of terminals referred to as differentiated wave terminals, apparatus interposed between the first and second pairs of terminals for converting the input cycle of voltage fiuctuationjinto a sharp voltage impulse, a third pair of terminals referred to as integrated wave terminals, a resistance capacity coupling circuit interposed between said input terminals and said integrating tenminals, said coupling circuit having a relatively high prodnot of resistance and capacity, including a coni denser connected between the integrated wave terminals and a resistor connected between one of said integrated wave terminals and one of the input terminals, the remaining input terminals, the remaining integrated wave terminal and one of the differentiated Wave terminals being concoupling device and mixer interposed between the diiferentiated 'wave terminals and the output terminals on the one hand and between the integratedwaveterminals andlthe output terminals onthe other hand, said coupling device having the characteristic of passing an impulse only whentthe voltages applied thereto exceed predetermined values, whereby the reception of a genuine signal prepares the coupling device for the passing of the sharpened genuine wave appearing at the difierentiated wave terminals by applying an integration of the genuine wave to the integrated wave terminals but spurious voltage fluctuations are of insufiicient time duration per cycle tolproduce an integrated wave of sufficient value to prepare the coupling device for impulse transmission.

l -3. A discriminatingimpulse transmitter comprisinga pair of input terminals to which a voltage fluctuation is adapted to be applied as an input impulse, a second pair of terminals referred to as differentiated wave terminals, appa'ratusinterposed between the first and second pairs of terminals for converting. the input cycle of voltage fluctuation into a sharp voltage impulse, a third pair of terminals referred to as integrated wave-terminals, a fourth pairof terminalsreferred to as output terminals and a coupling device interposed between the differentiated wave terminals and the output terminals on the one hand and between the integrated wave terminals and the output terminals on the other hand, said coupling device having the characteristic of passingan impulse only when the voltages applied thereto exceed predetermined values.

4. A. discriminating impulse transmitter comprising a pair of input terminals to'which a voltage fluctuation is adapted to be appliedcas an input impulse, a second pair of terminals referred to as integrated wave terminals, an integrating device interposed between the input terminals and the integrated wave terminals for producing a wave having an amplitude continuously proportional to the integrated value of a wave applied to the input terminals, a third pair of terminals referred to as output terminals, and a coupling device interposed between the said input terminals and the output terminals separately from said integrated wave terminals and said integrating device, said coupling device having, however, a voltage responsive control element for rendering the coupling device effective or inefiective, said voltageresponsive element being connected to said integrated wave terminals for rendering the coupling device effective only when the potential difference between the integrated wave terminals equals the integrated value of waves of a minimum effective period which are to be transmitted by the coupling device.

'5. A discriminating impulse transmitter comprising a pair of input terminals to which a voltage fluctuation is adapted to be applied as an input impulse, a second pair of terminals referred to as diiierentiated wave terminals, a clipper for converting the input wave into a square topped wave with a relatively steep cross-over portion, a device interposed between the clipper and'the differentiated wave terminals for generating a steep voltage impulse at the differentiated wave terminals in response to the cross-over portion of the clipped wave, a third pair of terminals referred to as integrated wave terminals, a device interposed between the input terminals and the integrated wave terminals for producing a wave hav-' ing an amplitude continuously proportional to the integrated value of a wave applied to the input terminals, and a mixer having a pair of control electrodes one of which is connected to the diiferfor passage of an impulse, whereby such noise voltages and spurious voltage fluctuations are cut oil from the output of the mixer.

6. Apparatus for transmitting voltage fluctuations applied between a pair of conductors and substantially eliminating line to ground noise or spurious voltages picked up between said conductors and ground, said circuit comprising a pair of input terminals to which said conductors may be coupled, a pair of three-element discharge de-' vices connected push pull, a ground terminal and an energizing source terminal between which a source of anode potential may be applied, said electric discharge devices each having an anode, a cathode and a control electrode, a coupling between said input terminal and said control electrodes for applying a potential difference between said control electrodes responsive to the potential difference between said input terminals, an impedance connected between said cathodes and said ground terminal, a pair of anode impedances each connected between said anode source terminal and one of said anodes, and an output terminal connected to one of said anodes, whereby the output voltage between said output terminal and said ground terminal fluctuates in response to variations in voltage applied between said input terminals with line to ground noise eliminated, said desired input voltage having the effect of raising the potential of one control electrode and lowering the potential of the other at any given instant to maintain substantially constant current in the cathode impedance and consequently substantially constant ratio of amplification whereby line to ground noise produces simultaneous variation in the same direction of the control electrode potentials to produce variationin current flowing in the cathode impedance whereby degenerative amplification is introduced and such line to ground voltage is attenuated.

7. A test impulse generator for an impulse responsive device comprising a rotating member carrying a permanent magnet, a current-conducting coil mounted adjacent said rotating member in inductive relation with said magnet atone angular position of the rotating'member and a substantially constant speed motor for driving said rotating member with means for measuring the speed of said motor whereby the timing of electrical impulses induced in said current-conducting coil by the motion of said magnet may be compared with the measured speed of the driving motor.

8. A wave converting circuit comprising a three-element zero-biased grid-limited electric discharge device with an anode energized through an anode impedance, said device having a cathode and a control grid joined by a resistor across which a reversing polarity peaked wave is adapted to be applied, a pair of output terminals and a resistance-capacity wave-sharpening coupling between the electric discharge device and the output terminals, said coupling having a relatively small time constant, whereby the positive peaks of the wave applied to the said control electrode are relatively ineffective and the negative peal;

drives the discharge device abruptly beyond cut- 17 ofl to transmit'a sharp positive peak of increased slope to the said output terminals.

9. A wave converting circuit for producing a single steep positive peak at the zero cross-over point of a cycle of voltage fluctuation comprising a pair of input terminals to which an input voltage fluctuation cycl is adapted to be applied, an intermediate terminal, a resistor connected between the first of said input terminals and said intermediate terminal and a condenser of relatively small capacity connected between the remaining .inputterminal and said intermediate terminal, a grid-limited zerobiased electric discharge devicehaving an .anode, a cathode and-fa control grid, the resistance of said first mentioned resistor exceeding the grid to cathode resistance of said discharge device, an anode r'esistor adapted to be connected in series between the anode and the positive terminal of an anode voltage source having a negative terminal connected to the cathode of the discharge device, said cathode being connected to the first of said input terminals and the control electrode being connected to said intermediate terminal whereby a diflerentiation of the input wave applied to the input terminals appears between the first input terminal and the intermediate terminal, and the positive peaks of said difierentiated wave have relatively little efiect on said electric discharge device owing to its characteristic of being effectively saturated at zero grid potential by the rectifying efiect of the control grid tending to limit its positive potential, but the negative peak of the differentiated wave is inverted to form a positive peak appearing at the anode of the electric discharge device, the time constant or resistancecapacity product of said differentiating resistor and condenser being small in relation to the expected time duration of negative input impulses for permitting the control grid to return to within negative cut-ofi potential and thus to restore the anode potential to th initial value before the end of the input impulse, thereby making the output pulse duration and shape as well as amplitude independent of input impulse shape and duration.

V PHILIP C. MICHEL. 

